In such ignition coils, it is well known that, because the secondary circuit produces a very high electrical voltage, it is necessary to provide, between the secondary winding and all other metallic elements of the coil, a gap which is sufficient to give the largest possible high tension paths, so as to avoid the occurrence of an electric arc between the secondary winding and any of the other above mentioned metallic elements.
This problem is especially hard to overcome in existing types of ignition coil, since the primary and secondary windings are arranged coaxially on the central magnetic core. Thus, during assembly of the coil, the fitting of the primary assembly into the secondary assembly must be carried out very precisely, in order that the spacing in all directions between the primary and the secondary will be of exactly the correct dimensions.
Another problem that has to be overcome is that of how to retain the primary assembly in place in the secondary in such a way that, when the resin is being injected into the casing, the primary assembly remains securely in position with respect to the secondary assembly.
Finally, the fitting and securing of the primary assembly needs to be carried out in as simple a way as possible, so as to satisfy the economic requirements of mass production of such coils.